Stability analysis of ‘roof-coal pillar’ structure in longwall multi-section mining of steeply dipping coal seam

Abstract

To solve the problem of stability control of coal pillar in steeply dipping coal seam (SDCS), based on the characteristics of surrounding rock structure and stress environment of the coal pillar, a special bearing structure of ‘roof-coal pillar’ combination is proposed through theoretical analysis. The mechanical model of inclined ‘roof-coal pillar’ structure is established, and the stress and strength characteristics of each element in the structure are deduced. Combining numerical calculations (PFC2D-FLAC2D coupling model) and physical similarity simulation, the stress evolution characteristics and failure mechanism of the ‘roof-coal pillar’ structure under the influence of mining were revealed. The results show that the coal pillar of SDCS is easy to form a ‘roof-coal pillar’ combined bearing structure with the roof strata. Under the influence of mining, the stress distribution and deformation evolution within the ‘roof-coal pillar’ structure show strong non-uniform and asymmetric characteristics. Among them, the stress distribution shows an ‘ellipse’ shape which is offset to the upper section, and the main deformation zone of the structure is a diagonal deformation distribution zone that runs through the coal and rock in the same direction as the stress offset. The failure of the ‘roof-coal pillar’ structural firstly occurs in the coal area near the coal-rock interface on the side of the lower section, and finally forms a diagonal failure crack running through the coal and roof, which is manifested as a diagonal shear failure mode. The findings can provide a theoretical basis for the stability control of coal pillars in multi-section mining of SDCSs and improve the safety production technology level of the working face.

Keywords

• Steeply dipping coal seam
• multi-section mining
• ‘roof-coal pillar’ structure
• stability analysis
• failure mechanism